The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
An optical lens is generally manufactured in accordance with wearer specifications. In the case, for example, of an ophthalmic lens for the correction or improvement of eyesight, the ophthalmic lens is manufactured according to a wearer prescription corresponding to the visual requirements of that wearer. In addition, the shape and size of the spectacle frame supporting the ophthalmic lens is taken into account. At least one of the surfaces of the ophthalmic lens is processed to provide an ophthalmic lens according to the wearer prescription. The contour of the ophthalmic lens is edged according to the shape of the spectacle frame on which the ophthalmic lens is to be mounted.
An optical lens is generally manufactured from an optical lens blank such as a semi-finished lens blank. A semi-finished lens blank generally has two opposite surfaces at least one of which is unfinished.
The unfinished surface of the lens blank is machined according to the wearer's prescription to provide the required surface of the optical lens. An optical lens having finished back and front surfaces is often referred to as an uncut optical lens. The uncut optical lens is edged according to a shape of a spectacle frame of the optical lens in order to obtain an edged or cut optical lens.
According to further manufacturing processes an optical lens may be obtained by machining both surfaces of an optical lens blank.
With the increasing trend to larger and larger spectacle frames, for example wrap or shield style spectacle frames, the problem of producing optical lens from optical lens blank is more and more complex.
For example as illustrated on FIG. 1, in the case where the frame on which the optical lens 10 is to be mounted is shaped such that the nasal (d2) and temporal (d1) distances, respectively defining the distance between the optical reference point OP and the nasal and temporal edges, are dissymmetric, a lens blank having a significantly larger diameter is required in order to be of sufficient size to enable an optical lens of the required size to be obtained.
This leads to wastage of the optical material of the optical lens blank.
Therefore, it appears that there is a need to for a method for determining the most appropriate lens blank to be used for manufacturing a given finished optical article, such as a optical lens.